Chromate treatments etch primers

While etch primers, also known as pretreatment primers and wash primers, can be regarded as priming paints which promote their own adhesion by etching the metal surface, they may also be regarded as phosphate/chromate etching treatments which leave an organic residue on the surface to form the basis of the subsequent paint scheme. A detailed account of the etch primers has been given by Coleman . 

Chemical treatments are usually most effective with aluminum alloys, especially when long-term environmental exposure is required. The sulfuric acid—dichromate etch FPL etch, named after Forest Products Laboratory, US Department of Agriculture www.fpl.fs.fed.us) has been used successfully for many decades. Techniques more recently developed are often modifications of the FPL procedure. Other important methods include chromate conversion coating and anodizing. Corrosion-resistant adhesive primer, as well as anodic and chromate conversion coatings, helps to prevent corrosive failure of adhesion. ... 

---